Improvement im sum-dials



Jj bavure.

Sun-Dials..

. Patented De,.8,1874.

UNITED STATES PATENT OFFICE.

JoHN DEvLiN, 0E rHILADELPHIA, PENNSYLVANIA.

IMPRQVEMENT sua-DIALS.

Specification forming partof Letters Patent No. 157,586, dated December8, 1874.; application filed August l1, 1874.

simple and inexpensive automatically-actingA instrument whereby themeridian time and the degree from which to compute latitudev of thelocality of the device will, without lifting or handling the same, bedistinctly and accurately shown by the shadow of a magnetic needlepoised horizontally upon a vertical support fixed in the apex of ahemisphere, marked by a series of equidistant latitudinal lines frombase to apex, and the lines and intermediate spaces divided and numberedon a longitudinal line, to indicate degrees from l to 90, as will bemore clearly explained, with reference to the accompanying drawings, inwhich- Figure 1 is a perspective view of my said indicator, secured upona circular platform and covered by a glass shade. Fig. 2 is a plan Viewof Fig. l. Fig. 3 is a side view of the magnetic needle, enlarged.

'lhe hemisphere A is made of wood, or any other suitable material, andis circumscribed by latitudinal lines at equal distances apart, andcommencing at its base, thus dividing its surface from base to apex intonine equal parts, which are numbered from 10 to 90, inclusive, from thefirst line above its base to its apex, along a longitudinal line, a',which is marked by a series of short horizontal lines, dividing eachspace between the latitudinal lines into five equal parts, eachindicating two degrees. The magnetic needle B is a straight bar ofsteel, about twice as wide as it is thick, and one-fifth longer than thediameter of the hemisphere A. It has a conical cavity in the mid-lengthof its lower edge, which extends nearly to the opposite or upper edge,whereby it is supported edgewise and horizontally, so as to swing freelyupon the. point of the vertical pole or stem C, at a short distanceabove the apex of the hemisphere A, as represented in Fig. l. Theindicating end of the magnetic bar B has a short slender' bar of steel,b', fixed at right angles to the sides of said bar, so as to projectfrom each side to the length of about one-eighth of the length of saidmagnetic bar B, and is secured in position by `means of a smallbinding-screw, bo, in the said end of B. The opposite end of B isslotted to receive an adjusting-screw, b, provided with a head, andadapted to be readily screwed inward and outward in bringing the needleB into equipoise, or true horizontal position, upon its support C. Thebottomof the hearinghole in the mid-length of B is intended to bejeweled, in order to reduce friction as much as possible, that themagnetic needle may 'come to thegnorth and south directions withfacility.

The proportions of the different parts of my said invention should be asfollows, viz: lf the diameter of the hemisphere A be live inches, thelength of C should be one-eighth of an inch for each inch of saiddiameter of A, and the length of the magnetic needle B onefifth longerthan said diameter, or six inches, and the length ofthe cross-bar babout onefourth of that of the magnetic needle B. These proportionallengths are for all sizes of the hemisphere; and the larger the same maybe, the moredistinct and observable will be the indications.

The device shown in the drawings is specially adapted for the northernhemisphere of the earth only. For the southern hemisphere, the oppositeend of the magnetic needle B must be fitted with the cross-bar b', andthe longitudinal line of degrees a also made on the opposite side of thehemisphere, or the said hemisphere rotated half-way around, because therays of the sun will come from the opposite direction in this case.

When the invention is to be used in both hemispheres, it is intended tohave both ends of B provided with a cross-bar, b', and the hemisphere Awith two like lon gitudinall scales,

In using 'my said device or apparatus, it must be placed so as to restwith the base of the hemisphere A in a true horizontal plane, and withthe longitudinal line of the scale a coincident with the north and southdirection of the magnetic needle B when the latter is at rest in itsproper horizontal position, as represented in Figs. l and 2. Now, whenmeridian time arrives, the shadow of the indicating end of the magneticneedle B will correspond precisely with the longitudinal line of thescale a', and the two ends of the curved shadow of the cross-bar b willbe at the degree-line corresponding with the altitude or declination ofvthe sun, and thus the true degree for computing therefrom the latitudeof the place of observation.

The shadow of the magnetic bar B on the hemisphere A from the vernalequinox, March 20, descends on said. hemisphere one degree for eachdegree the earth moves its pole toward the sunabout twenty-three degreesto June .2lwhich gives seventeen degrees latitude from the celestialequator. The shadow now returns with the earth, and in ninety-two daysgets to the autumnal equinox, September 21 or 22; and when the earth hasmoved its pole its greatest distance, December 21, the shadow of thesaid magnetic bar will be about at sixty-three degrees from the equator,or twenty-seven degrees polar distance. From the equinoctial degree oflatitude either way (north or south) there are ninety-two days, nearly.Now, as four days give one degree declination, ninety-two days dividedby four equal twenty-three degrees; and as one day is equal to oneminute of time, so is four days to a degree of declination, and one dayor minute seventeen and one-fourth miles, which,

multiplied by four, gives sixty-nine miles to one degree.

Refraction ofthe suns rays by the glass cover is not appreciable inobserving the shadow of the magnetic bar or needle B; but, as it isintended merely as a protective cover, it may be simply lifted offbefore taking the meridian time and latitude, if it be desirable.

For use at sea, the whole apparatus is in tended to be suspended bygimbal-rings, in the same manner as a marine compass.

I claim as my inventionl. The automatic indicator, consisting of thehemisphere A, provided with the series of latitudinal lines and thelongitudinal scale of degrees, and also with the vertically-projectingstem C, as set forth, in combination with a magnetic bar, B, balancedand swinging freely upon the top of said vertical stem C, in the mannerand for the purpose hereinbefore described.

2. The adjusting-screw b, in combination with the slotted or recessed`end of the magnetic bar B, substantially as and for the purposeherei-nbefore set forth and described.

' JOHN DEVLIN.

Witnesses:

BENJ. MoRIsoN, WM. H. MonIsoN.

